Borehole opener

ABSTRACT

Borehole opener, particularly for enlarging this hole underneath a casing in the field of oil prospecting, comprising a body ( 2 ) of longitudinal axis ( 3 ), a duct ( 4 ) for drilling fluid, formed longitudinally in the body ( 2 ), and at least two hole-opening arms ( 5 ) which have an active part ( 7 ) equipped with cutting means ( 8 ), which are distributed symmetrically in the body ( 2 ) about the longitudinal axis ( 3 ), and which are arranged therein in such a way that they can be moved between a position of rest ( 9 ) in the body ( 2 ) and an active position ( 10 ) partially out of the body ( 2 ); in this hole opener in order to move it from the position of rest ( 9 ) to the active position ( 10 ), each arm ( 5 ) has a face ( 12 ), internal to the body ( 2 ), designed to be subjected directly, in the same way as an active face of a piston, to the pressure of the drilling fluid flowing through the body ( 2 ).

CROSS REFERENCE TO RELATED APPLICATIONS

Applicants claim priority under 35 U.S.C. § 119 based upon BelgiumApplication No. 09900163 filed 9 Mar. 1999.

BACKGROUND OF THE INVENTION

The present invention relates to a borehole opener, particularly forenlarging this hole underneath a casing in the field of oil prospecting,the hole opener comprising a body of longitudinal axis, a duct fordrilling fluid, formed longitudinally in the body, and at least twohole-opening arms which have an active part equipped with cutting means,which are distributed symmetrically in the body about the longitudinalaxis, and which are arranged therein in such a way that they can bemoved between a position of rest in the body and an active positionpartially out of the body.

BACKGROUND OF THE PRIOR ART

Prospecting for oil of natural gas, for example, requires the probing ofincreasingly deep depths. What is more, it is desirable to drill withsmall diameters so as to reduce the drilling time and tooling costs. Thecounterpart to this is an increase in pressure drop for the drillingfluid flowing between the wall of the hole and the drilling string andtherefore a reduction in the ability to remove particles of formation asa result of the lack of circulation of the drilling fluid at asufficiently high flow rate. As a result, control over the equivalentdensity of the sludge formed by the drilling fluid and these particlesof formation can rapidly be lost. This equivalent density gives rise toa pressure which may be desirable at certain formations, in order tosomewhat shore up the bored wall, and is therefore usually monitored tomake sure that this pressure does not exceed a value above which atleast this bored wall is excessively contaminated with the sludge and/oris excessively damaged in terms of its texture and composition and/ormay even be destroyed.

In order to avoid these problems with the bored wall, it is alsonecessary to be able easily to adjust this equivalent density. This thenentails improving the circulation of the sludge so as to encourage theremoval of particles of formation which would build up in the hole andwhich would have an adverse influence on the equivalent density.

To achieve this it is known practice possibly to make use of aconventional hole opener, with moving arms, which can enlarge thediameter of the hole already bored to up to twice its original size.Hole openers known to date comprise mechanisms, of the hinge andpivot-pin type, which are rather delicate to be used at a high rate ofadvance and are too long to be placed between the drill bit and, inparticular, an angled coupling well known to those skilled in the artand employed for directional drilling.

Drill bits with two offset longitudinal axes (bi-center bits) and pilottools (pilot bits) associated with boring tools and comprising ahole-opening fin fixedly projecting from the rest of the bit are alreadyknown. These devices are able to open out the hole at the same time asboring it. However, because of their asymmetric structure, these deviceshave an imbalanced behavior and because of this produce vibrationalforces which are detrimental to the mechanisms to which they are coupledand to the condition of the bored hole. What is more, because of this,these devices frequently cause unacceptable deviations in the boredholes.

SUMMARY OF THE INVENTION

The object of the present invention is to overcome the problems set outhereinabove and to propose a hole opener with moving arms which iscompact and robust and the mechanism of which involves a very smallnumber of moving parts, these advantageously having to be easy to removeand replace in the event of an incident occurring during operation. Whatis more, the hole opener of the invention is to have a small bulk in thelengthwise direction, so that it can readily be installed very near adrill bit, in a drill string, between the drill bit and theaforementioned angled coupling.

Underlying the invention, prior research was carried out into the amountof opening needed to solve the problem, explained hereinabove, ofremoving of sludge. Surprisingly, it was found that opening the hole outto a diameter approximately 10 to 20% greater, for example, than that ofthe casing or the nominal diameter of the associated drill bit, wassufficient to achieve this.

The problem of simplifying the mechanism was solved, according to theinvention, by choosing that, inorder to move it from the position ofrest into the active position, each hole-opening arm has a face,internal to the body, designed to be subjected directly, in the same wayas an active face of a piston, to the pressure of the drilling fluidflowing through the body.

According to one embodiment of the invention, each arm is kept in theposition of rest in the body, prior to a hole-opening operation, by atleast one pin designed to break when the pressure of the drilling fluidflowing through the body exceeds a predetermined value higher than amaximum usual boring value.

Operations of troubleshooting, removing and replacing any problematicalparts are simplified by choosing to mount the arm in the body by meansof an intermediate support which acts as a housing for the arm in thebody and which is fixed to the latter. As a preference, the intermediatesupport, the arm, elastic means for returning the arm into the body andthe pin constitute an assembly designed to be assembled in advanceoutside the body and then installed therein.

Other details and particular features of the invention will becomeapparent from the appended claims and from the description of the holeopener of the invention, which description is given hereinbelow by wayof nonlimiting example with reference to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows, in axial section, a hole opener of the invention, an armvisible in the figure being in the position of rest.

FIG. 2 shows a partial axial section in which the visible arm is in theactive position.

FIGS. 3 and 4 each show a cross section in which three hole-opening armsare depicted in the position of rest, and in the active position,respectively.

FIG. 5 shows, to a larger scale and in longitudinal section, an assemblycomprising an arm and an intermediate support so that arms can bemounted and exchanged quickly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the various figures, the same references denote similar or analogouselements

The hole opener 1 of the invention, as depicted by way of example inFIGS. 1 to 4, comprises a body 2 of longitudinal axis 3, a duct 4 fordrilling fluid, formed longitudinally in the body 2, and at least twohole-opening arms 5 which are distributed symmetrically in the body 2about the longitudinal axis 3 to make sure that the operation of thehole opener 1 is approximately balanced. FIGS. 3 and 4 show that threearms 5 can easily be arranged in the body 2 with angles of 120° betweentwo successive arms 5.

The arms 5 each have an active part 7 equipped with cutting means 8(FIGS. 3 to 5) which are known and explained hereinbelow. The arms 5 arearranged in the body 2 so that they can be moved between a position ofrest 9 in this body 2 and an active position 10 partially out of thissame body 2.

According to the invention, each arm 5 comprises, for moving it from theposition of rest 9 into the active position 10, a face 12 internal tothe body 2 and designed to be subjected directly, in the same way as anactive face of a piston, to the pressure of the drilling fluid flowingthrough the body 2. Through this arrangement, it is possible to avoidhaving intermediate mechanical parts between the fluid which is toactuate the arm 5 and this arm, and the problems known to those skilledin the art which may ensue.

The internal face 12 of the arm 5 should be understood as meaning anyface/surface in contact, at any moment in the drilling and/orhole-opening operation, with the pressurized fluid flowing through theduct 4. It is obvious that some of these faces/surfaces subjected to thesame pressure will compensate for each other but, overall, there remainsenough positive area that, for example with a positive pressuredifferential of the order of 2 MPa (about 300 psi) between the pressureof the fluid in the duct 4 and that of the fluid outside the body 2 inthe region of the arm or arms 5, a thrust force of the order of 2000 kgcan be obtained, in order to deploy the arm 5 from the body 2.

As a preference, the arm 5 is mounted in such a way that it can slideparallel to itself in the body 2, so as to move from the position ofrest 9 into the active position 10 and vice versa. The choice of amovement of this kind is one of the more favorable types of movement,for operation in the manner of a piston. A movement of pivoting about anaxis (not depicted) perpendicular to the longitudinal axis 3 and to thedirection of the travel of the arm 5, and arranged somewhat away fromthe arm 5 is, however, also possible, but would require special matchingof significantly higher cost than the matching of the previousembodiment in order to implement it.

In order to provide the aforementioned piston function, sealing means 11are provided at places which are known to those skilled in the art.

To move it from the active position 10 into the position of rest 9 whenthe pressure in the duct 4 decreases, each arm 5 advantageously engageselastic return means 13, for example compression coil springs 14 asdepicted in the drawings. This arrangement allows the hole opener 1 tobe withdrawn from the borehole without difficulty.

The arm 5 may, in the active position 10 out of the body 2, have aposterior face 16 (with reference to a direction of advance for openingout the hole) which is at an angle, designed, for example if the springs14 should be deficient, to help the arm 5 back into the body 2 when thehole opener 1 is being withdrawn from the borehole.

The arm 5 can be mounted in the body 2 by means of an intermediatesupport 15 which acts as a housing for the arm 5 in the body 2 and whichis fixed to the latter, for example by screws 17. Sealing means 18 maythen be provided between the body 2 and said intermediate support 15.

As a preference, prior to a hole-opening operation, each arm 5 is keptin the position of rest 9 in the body 2 by at least one pin 19 designedto break when the pressure of the drilling fluid flowing through thebody 2 exceeds a predetermined value higher than a maximum usual boringvalue.

For this purpose, the pin 19 may have a region 19A of calibratedweakness, at one or more points of transition 20 where the pin 19passes, as the case may be, either from the body 2 or from theintermediate support 15 into the arm 5. It is obvious that, unlike whathas been depicted in FIGS. 3 and 4, the pin 19 does not necessarily haveto emerge from both sides of the arms 5.

This pin 19 may fix the arm 5 merely to the intermediate support 15(FIGS. 3 and 4).

FIG. 4 shows the pin 19 broken into one part 19B in the arm and twoparts 19C in the intermediate support 15.

The intermediate support 15, the arms 5, the aforementioned elasticmeans 14 and the pin 19 may therefore constitute an assembly 21 (FIG. 5)designed to be assembled beforehand outside the body 2 and theninstalled therein. This then makes the hole opener 1 not only easier toassemble, but also easier to maintain or repair in the event of damage,etc.

On its outer face, between two successive arms 5, the body 2 may have alongitudinal passage 22 for returning drilling fluid to the surface, anda boss 23 arranged in this passage 22 so as to divert and/or deflect thedrilling fluid which is rising back up toward the surface onto that partof the wall of the hole on which the arms 5 are acting. The passage 22and the boss 23 are produced in such a way as not to form too great arestriction to the passage of the returning fluid.

It must be understood that the present invention is not in any wayrestricted to the embodiments described hereinabove and that manymodifications may be made thereto without departing from the scope ofthe claims given hereinbelow.

In the preferred embodiment of the hole opener 1 of the invention, thetravel of an arm 5 between the position of rest 9 and the activeposition 10 is limited in both directions of travel by stops. In theposition of rest 9, the arm 5 is usually completely retracted into thebody 2 and is held therein by reciprocal stop surface 25 (FIG. 3) or, asappropriate, by the pin 19. In the active position 10, the arm 5,retained by reciprocal stop surface 26 (FIGS. 2 and 4), sweeps throughan area, the largest diameter of which is equal to between 1.05 and 1.3times, preferably 1.2 times the nominal diameter of a drill bitassociated with the hole opener 1 for a combined drilling andhole-opening operation.

The cutting means 8 on the arms 5 are arranged by the person skilled inthe art in such a way as, for example, to obtain cutting efficiencysimilar to that of the cutting means of the associated drill bit.

The reciprocal stop surfaces 26 may be arranged on exchangeable oradjustable elements so as to allow a user of the hole opener 1 to choosethe extent to which the arms 5 can deploy out of the body 2 duringservice.

Key to the figures

-   1 hole opener-   2 body-   3 longitudinal axis-   4 duct-   5 hole-opening arms-   7 active part-   8 cutting means-   9 position of rest-   10 active position-   11 sealing means-   12 internal face-   13 elastic return means-   14 coil springs-   15 intermediate support-   16 posterior face-   17 screws-   18 sealing means-   19 pin-   19A weakened region(s)-   19B part of the pin-   19C part of the pin-   20 transition point-   21 assembly-   22 longitudinal passage-   23 boss-   25 reciprocal stop surfaces-   26 reciprocal stop surfaces-   S direction of advance of a hole-opening/boring process

1. A hole opener, particularly for enlarging the borehole underneath acasing, comprising: a body of longitudinal axis, a duct for drillingfluid, formed longitudinally in the body, at least two hole-openingarms, each arm having an active part equipped with cutting meansdistributed symmetrically in the body about the longitudinal axis andarranged in such body in a way that said arms can be moved between aposition of rest in the body and an active position partially out of thebody, wherein, in order to move said arms from the position of rest intothe active position, each arm has a face, internal to the body, designedto be subjected directly to the pressure of the drilling fluid flowingthrough the body, and wherein, to move the arms from the active positioninto the position of rest, the hole-opener comprises an elasticallyeffective return for returning the arms to the position of rest.
 2. Thehole opener as defined in claim 1, wherein at least one of said arms ismounted in such a way that said at least one arm can slide parallel toitself in the body so as to move from the position of rest into theactive position.
 3. A hole opener, particularly for enlarging theborehole underneath a casing, comprising: a body of longitudinal axis, aduct for drilling fluid, formed longitudinally in the body, at least twohole-opening arms, each arm having an active part equipped with cuttingmeans distributed symmetrically in the body about the longitudinal axisand arranged in such body in a way that said arms can be moved between aposition of rest in the body and an active position partially out of thebody, wherein, in order to move said arms from the position of rest intothe active position, each arm has a face, internal to the body, designedto be subjected directly to the pressure of the drilling fluid flowingthrough the body, wherein each arm is temporarily kept in a position ofrest by at least one pin designed to break when the pressure of thedrilling fluid flowing through the duct exceeds a predetermined value.4. A hole opener as defined in claim 3, wherein at least one of saidarms is mounted in the body by means of an intermediate support whichacts as a housing for said at least one arm in the body and which isfixed to said at least one arm.
 5. A hole opener as defined in claim 4,wherein the aforementioned pin fixes said at least one arm to saidintermediate support.
 6. A hole opener as claimed in claim 5, whereinthe intermediate support, the at least one arm, the aforementionedelastically effective return and the pin constitute an assembly designedto be assembled in advance outside the body and then installed in thebody.
 7. A hole opener as defined in claim 3, wherein at least one ofsaid arms is mounted in the body by means of an intermediate supportwhich acts as a housing for said at least one arm in the body and whichis fixed to said at least one arm.
 8. A hole opener, particularly forenlarging the borehole underneath a casing, comprising: a body oflongitudinal axis, a duct for drilling fluid, formed longitudinally inthe body, at least two hole-opening arms, each arm having an active partequipped with cutting means distributed symmetrically in the body aboutthe longitudinal axis and arranged in such body in a way that said armscan be moved between a position of rest in the body and an activeposition partially out of the body, wherein, in order to move said armsfrom the position of rest into the active position, each arm has a face,internal to the body, designed to be subjected directly to the pressureof the drilling fluid flowing through the body, wherein each arm istemporarily kept in a position of rest by at least one pin designed tobreak when the pressure of the drilling fluid flowing through the ductexceeds a predetermined value wherein the pin comprises a region ofcalibrated weakness.
 9. A hole opener, particularly for enlarging theborehole underneath a casing, comprising: a body of longitudinal axis, aduct for drilling fluid, formed longitudinally in the body, at least twohole-opening arms, each arm having an active part equipped with cuttingmeans distributed symmetrically in the body about the longitudinal axisand arranged in such body in a way that said arms can be moved between aposition of rest in the body and an active position partially out of thebody, wherein, in order to move said arms from the position of rest intothe active position, each arm has a face, internal to the body, designedto be subjected directly to the pressure of the drilling fluid flowingthrough the body, wherein on an outer face, between two successive arms,the body has a longitudinal passage for returning drilling fluid, and aboss arranged in this passage so as to define the drilling fluid ontothat part of the wall of the borehole on which the arms are acting. 10.A hole opener as defined in claim 3, wherein the travel of at least onearm between the position of the rest and the active position is limitedby stops, and also by the pin so that in the position of rest, said atleast one arm is fully retracted into the body and so that in the activeposition, said at least one arm sweeps through an area, the largestdiameter of which area is equal to between 1.05 and 1.3 times thenominal diameter of a drill bit associated with the hole opener for acombined drilling and hole-opening operation.